$2\mathrm{.}7$: A car is stopped at a traffic light. It then travels along a straight road such that its distance from the light is given by x$($t$)=$bt$^2-$ct$^3,$ where b$=2,4$m$/$s$^2$ and c$=0\mathrm{.}120$ m$/$s$^3.$ Calculate the average velocity of the car for the time interval t$=0$ to t$=10\mathrm{.}0$s$.$ Calculate the instantaneous velocity of the car at t$=0,$ t$=5\mathrm{.}0$s$,$ and t$=10\mathrm{.}0$s$.$ How long after starting from rest is the car again at rest?